Manufacture of shaped products impermeable to moisture



Patented Jan. 24, 1939 MANUFACTURE OF SHAPED. rnoDUo'rS IMIERMEABLE 'ro MOISTURE Wal er Kiinig, Wiesbaden, Germany, assignor to RudUlPh Koepp & Co. Chemische Fabrik A. G., Oestrich in Rheingau, Germany, a German company No Drawing. Application September 8, 1936, Se-

rial No. 99,850. 1935 3 Claims.

This invention relates to a process for the manufacture of shaped products impermeable to moisture from cellulose esters.

A disadvantage for many purposes of applica- 3 tion of the known thin sheets of celluloseor its derivatives is that they are to a certain extent permeable to-water or water vapour. Attempts have been made to overcome this disadvantage by coating the sheets with a varnish, the fundamental constituent of which mostly consists of cellulose derivatives dissolved in the usual organic solvents and which contains in addition waterrepelling agentssuch as resin's, softeners, waxes and the like. The thin sheets so prepared are, it

5 is true, practically impermeable to water at the outset, but have the unpleasant property that the coating. even after only short contact with water readily becomes detached.

Attempts have also been made to overcome this :0 latter disadvantage. Thus, for example, it has already been proposed first to treat thin sheets of cellulose, cellulose hydrate or cellulose ethers with organic liquids which are miscible with water and have a swelling effect on cellulose gels 35 and, after removing the said liquids, to coat the sheets in a manner known per se with varnish.

According to this invention it has been found that thin sheets of cellulose esters, particularly cellulose formate, may be provided with coatings,

50 which adhere satisfactorily to the sheets in the presence of water or moisture, by pre-treating the sheets with "mixtures which contain formic acid as swelling agent and substances, which do not dissolve the sheets, and thereafter coating the sheets so pro-treated with water-repelling substances.

Depending on the cellulose ester, of which the thin sheet consists, acetone, butyl acetate, toluene and the like known reagents, may be employed as substances which do not dissol e the sheets. Whereas formic acid by itself completely dissolves cellulose formate, in admixture with the substances which donot dissolve the cellulose formate, for example acetone, butyl acetate and 45 the like, it exerts'a swelling and occasionally a slight dissolving action on the cellulose formate sheet and thus constitutes an excellent medium between the varnish to be subsequently applied and the sheet as base. The coating is conse- 50 quently firmly and intimately fixed on the sheet, so that it does not, or only with great difficulty, become detached from the latter, even after being immersed in water'for several hours.

After the swelling pre-treatment and preferi ably without removing the mixtures containing In Germany September 30,

swelling agents from the sheets, the latter are coated with a covering varnish, which consists for example of cellulose esters, resins, softeners and waxes dissolved in acetone, butyl acetate, ethyl acetate and the like, for example by dipping, 5 spraying, painting or in any other suitable manner and finally dried at ordinary, or preferably elevated, temperature. The solvents vaporized thereby may be recovered by the usual processes.

In some cases varnishes may be used, to which there have been added agents having a swelling action on the sheets, for example the same swelling agents as have been used for the pre-treatment of the sheets. A coating is obtained which, even after the sheets have been immersed for several hours in water, does not become detached and is practically impermeable to water and moisture.

In addition to thin sheets of cellulose formate, any other cellulose ester sheets, for example sheets of cellulose acetate, which are swollen and possibly dissolved by the admixtures employed, may also be treated in accordance with the process of this invention, both when employing formic acid and also when employing other admixtures.

Examples 1. Acellulose formate sheet is drawn through a mixture of equal parts by weight of concentrated formic acid and butyl acetate. Without removing the adhering solvent, the sheet so pre-treated is then coated with a varnish which contains 3.4 parts by weight of nitrocellulose, 0.87 part by weight of a high boiling phenol ether, 77.04 parts by weight of butyl acetate, 10.0 parts by weight of concentrated formic acid, 1.74 parts by weight of shellac and 6.95 parts by weight of alcohol.

2. A cellulose acetate sheet is pre-treated with a mixture which consists of 85 parts by weight of toluene, 10 parts by weight of spirits and 5 parts by weight of formic acid. The sheet is then dried and coated with a varnish which contains 2.0 parts by weight of nitrocellulose, 1.0 part by weight of shellac solution, 0.6 part by weight of a high boiling phenol ether, 0.4 part by weight of an alkyd resin, 1.0 part by weight of tricresyl phosphate, 18.0 parts by weight of alcohol, 6.5 parts by weight of ether, 3.0 parts by weight of toluol and 5.0 parts by weight of formic acid.

What I claim is:

1. A process for the production of water impermeable, shaped cellulose formate products which are provided with a single water-impermeable coating bonded directly to the cellulose formate base which comprises treating the shaped cellulose formate products with a mixture which contains formic acid as a swelling agent and an inert volatile diluent free from dissolving action on the shaped cellulose formate products and thereafter coating the shaped products with a varnish containing water-repelling substances without removing the absorbed portion of the swelling agent.

2. A process for the production of water impermeable, shaped cellulose formate products which are provided with a single water-impermeable coating bonded directly to the cellulose repelling substances, contains substances having 1 a swelling action on the shaped products.

WALTER KGNIG. 

